This invention relates to illuminating systems and particularly to graphic arts illuminating systems using gas discharge lamps and means and methods for energizing the lamps.
Such systems are used, for example, to illuminate color or black and white transparencies to be photographed by a camera, to illuminate originals to be copied by a camera, to illuminate transparencies in color enlargers, to expose plates or proofing or other photosensitive materials, and for other photographic graphic arts application.
Many of these systems utilize gas discharge lamps such as Xenon filled quartz lamps, as light sources because of their ability to emit large quantities of light in comparison with the amount of heat generated. However, a gas discharge lamp, when operated in a glow region, exhibits a negative resistance characteristic. A series impedance or ballast is used to prevent the lamp from drawing the vast quantities of energy which would ultimately destroy the lamp when it operates under these conditions. Such ballasts are costly and add substantial weight and bulk to the system.
Another method of preventing destruction of the lamp is to store energy during each cycle or half cycle of alternating voltage across a capacitor, and to apply the energy to the lamp in short high power pulses that drive the lamp into the arc discharge region. Effectively, this operates the lamp at instantaneous high powers but low average powers. This pulse mode of operation is frequently applied with Xenon filled quartz lamps. It produces high efficiency as measured in lumens per watt.
However, operating in the pulse mode requires expensive, bulky equipment, and requires operating at power factors less than unity.
An object of the invention is to overcome these disadvantages.
Another object of the invention is to lower the weight and bulk of such systems, and methods and means of driving the lamps in such systems.